The disclosures of Japanese Patent Applications No. 2000-380683 filed on Dec. 14, 2000, No. 2000-351565filed on Nov. 17, 2000, No. 2000-353161 filed on Nov. 20, 2000, and No. 2000-385751 filed on Dec. 19, 2000, each including the specification, drawings and abstract are incorporated herein by reference in their entireties.
1. Field of Invention
The invention relates to an evaporative fuel leakage preventing device for an internal combustion engine. More particularly, the invention relates to an evaporative fuel leakage preventing device capable of preventing evaporative fuel from being discharged to the atmosphere from an intake passage during stoppage of an internal combustion engine.
2. Description of Related Art
When an internal combustion engine is out of operation, evaporative fuel is generated in an intake passage of the engine for various reasons. For instance, if fuel supplied to a combustion chamber of a certain cylinder during operation of the engine fails to burn and accumulates in the cylinder when the engine is stopped, the fuel evaporates in the cylinder during stoppage of the engine, so that evaporative fuel is generated. Accordingly, if there is at least one cylinder with open intake valves during stoppage of the engine, evaporative fuel flows from the cylinder into the intake passage and fills it up. Further, if fuel adherent to a wall surface of an intake port in its liquid state during operation of the engine remains when the engine is stopped, the fuel evaporates during stoppage of the engine, so that evaporative fuel forms in the intake passage. In addition, in the case of an engine having fuel injection valves, a small amount of fuel accumulating in each fuel injection valve during stoppage of the engine may leak out to an intake passage and turn into evaporative fuel therein.
If evaporative fuel is thus generated in the intake passage during stoppage of the engine, the evaporative fuel thus generated fills up the intake passage and leaks out to the atmosphere from an opening (suction inlet) in the intake passage. In such a case, hydrocarbon and so on contained in the evaporative fuel may cause air pollution.
In order to prevent evaporative fuel from being discharged from the intake passage during stoppage of the engine (i.e., to prevent xe2x80x9cintake leakage emissionxe2x80x9d), there is proposed an evaporative fuel leakage preventing device that has an adsorbent such as activated carbon disposed in an intake passage of an engine and that causes the adsorbent to adsorb evaporative fuel generated in the intake passage during stoppage of the engine so as to prevent the evaporative fuel from being discharged to the atmosphere.
For example, Japanese Patent Application Laid-Open No. 11-82192 discloses one such evaporative fuel leakage preventing device. The evaporative fuel leakage preventing device disclosed in this publication has an adsorbent disposed between a throttle valve in an intake passage and a main body of an engine, and the adsorbent is capable of adsorbing evaporative fuel produced through evaporation of fuel leaking out from a fuel injection valve during stoppage of the engine. The evaporative fuel leakage preventing device disclosed in the publication is designed such that evaporative fuel generated in the intake passage, for example, during stoppage of the engine is adsorbed by the adsorbent and is thus prevented from being discharged therefrom to the atmosphere. Consequently, evaporative fuel is prevented from being discharged to the atmosphere during stoppage of the engine. Further, if the engine is operated next time, the adsorbent is desorbed (purged) of evaporative fuel adsorbed thereby due to intake air (sucked air) flowing through the adsorbent, and the evaporative fuel is supplied to the engine together with intake air and bums. Thus, the adsorbent is prevented from becoming saturated with evaporative fuel adsorbed thereby.
However, in the case of Japanese Patent Application Laid-Open No. 11-82192 mentioned above, evaporative fuel is discharged to the atmosphere from an inlet of the intake passage under certain circumstances and causes intake leakage emission. For example, if an adsorbent such as activated carbon or the like adsorbs evaporative fuel and then is heated up, it discharges a part of the adsorbed evaporative fuel due to a decrease in its evaporative fuel adsorbing capacity. Hence, the device disclosed in Japanese Patent Application Laid-Open No. 11-82192 has the following problem. Namely, if the ambient temperature rises during stoppage of the engine, a part of the evaporative fuel adsorbed by the adsorbent is discharged therefrom to the atmosphere through the inlet of the intake passage.
It is one object of the invention to find a solution to the aforementioned problems and provide an evaporative fuel leakage preventing device that prevents leakage of evaporative fuel when the adsorbent rises in temperature due to a rise in ambient temperature during stoppage of an internal combustion engine.
In order to achieve the aforementioned and/or other objects, one aspect of the invention provides an evaporative fuel leakage preventing device for an internal combustion engine in which an adsorbent for adsorbing evaporative fuel is disposed in an intake passage of the internal combustion engine, wherein the adsorbent adsorbs evaporative fuel generated in the intake passage during stoppage of the engine. In addition, the adsorbent is purged of the evaporative fuel adsorbed thereby due to intake air in the engine during operation thereof so that the evaporative fuel is sucked into the internal combustion engine. In this evaporative fuel leakage preventing device, an atmospheric suction inlet of the intake passage is formed on a side of the adsorbent opposite to a direction in which evaporative fuel generated in the intake passage moves due to application of a gravitational force. The adsorbent is purged (desorbed) of evaporative fuel adsorbed by the adsorbent due to intake air in the internal combustion engine during operation of the internal combustion engine, so that the evaporative fuel is sucked into a cylinder of the internal combustion engine.
That is, the above-mentioned evaporative fuel leakage preventing device is designed such that the adsorbent disposed in the intake passage of the internal combustion engine adsorbs and holds evaporative fuel produced through evaporation of fuel during stoppage of the engine, thus preventing evaporative fuel from being discharged to the atmosphere from the suction inlet. Further, if the ambient temperature rises during stoppage of the engine, a part of the adsorbed evaporative fuel is discharged from the adsorbent. However, since evaporative fuel is heavier than air, the discharged evaporative fuel accumulates in a region close to a lower portion of the adsorbent or is returned to the inside of the internal combustion engine due to application of a gravitational force. Thus, evaporative fuel does not flow out to the outside from the atmospheric suction inlet. Accordingly, generation of intake leakage emission during stoppage of the engine, that is, leakage of evaporative fuel, is prevented.